Here in New Mexico they have started implementing a voltage drop rule in residential wiring. Anything over 75', the wire has to be upsized. No more than 5% VD. My problem is that I think homes have been working just fine for the past 100 or so years. It is really going to jack up the price of wiring a home. Any thoughts?

and with all the varied turns and curves a run of romex takes in wending its way though a structure.. are you supposed to cut it @ 75 feet and just see where the wire runs out? I am still of two minds on this one.. yes houses have worked well for 100 years, but uses for electricity (as well as electricity usage) in homes has also changed in that time. Might be overkill, but why not build them to the best standards that the times allow? At the turn of the century a single 20A circuit was deemed adequate to supply an entire household, back in the days when consumer appliances consisted of: 1.incandescent lights, 2. incandescent lights, 3. incandescent.. there were no plasma tv's, kitchenaid mixers, conair blowdryers, garbage disposals or garage arcwelders (there weren't even cars to park inside.. garages were for horse carriages..) I think it is a lot cheaper to build in the capacity before the drywall goes on. Whatever it costs it is still cheaper than adding it years after or even hours after the drywall goes up.

As an aside, I am wondering if in 100 years our present power usage in homes won't be looked upon as just as quaint, not for how little we built into the building but for how much we built in. With more efficient and lower power consuming products coming out every day, as well as all the essentially DC stuff like computers & PV Cells.. who knows, maybe they will say in 100 more years that Edison was right with his DC power (!?!?!)

But to get back to the original point.. I don't think you can ever go wrong building it good and building it right, and keeping voltage drop under control is part of "building it right". What has me scratching my head a little is how this will be enforced by inspectors- seems a bit time consuming and opens a can of worms for determining what work on whose side of the line is at fault..I mean how does one accurately measure the lenght of a run once it is on the frame of the house? And if the VD is over the limit, you could also argue it a few ways to keep the issue going round-and-round, to no resolution. Sounds like a good idea on paper and also a goal worth striving for as the electrician, but I also see lots of gray area.

I think the old REA (now RUS I understand) used to recommend no more than 5% drop in the service entrance. By "entrance" they were defining it as transformer (including the transformer) to the meter. If you have a 2.5% impedance transformer, at full load you have already lost half your allowance.
Considering that some primary line voltage isn't that great to start with, they may have a point.

It's a little off topic, but we've always had problems with customers not wanting that "ugly" old transformer anywhere near their pretty new house, so they insist on a 250 foot service drop. A week later, they're complaining about their lights dimming when the AC comes on.

In my opinion, if a house is large enough to have 75-foot runs, a sub-panel is an option to be considered. With load diversification, a single feeder will exhibit less voltage drop than individual home runs.

My refigerator draws 2.5amps peak. Foolish to have a dedicated ciruit. More foolish to upsize the circuit.

I use a 50amp subpanel for every 600-700sqft in a residence. Keeps the voltage drop down. Makes it easy to NOT work on live circuits.

In the U.K., we have a requirement in our wiring rules which states that the voltage drop from service entrance terminals to the farthest point of utilization on a circuit under normal load should not exceed 4% (i.e. 9.6V on a 240V supply).

In fact it used to be even tighter, and at one time specified 2.5% plus 1 volt (7V on 240V).

Gentlemen:
VD is addressed within 210.19 (FPN)3% branch circuits, and 2% feeders, hence 5% total.

I was and am under the impression that (FPN's) are 'non-enforceable', and only advisory. On that note, did your location write a local amendment with the "5%"??

As an EC (commercial/ind) VD is an issue that I address 'as required' for my clients, not as an NEC requirement. Further, within plans and specs, the EE/Architect addresses his/her VD requirements, and they MUST be adhered to, unless they create an NEC conflict.

As an AHJ, I have to enforce the plans and specs, as they become part of the Electrical Permit, upon review and approvals.

The areas that I am familiar with are comm/ind; a 'large' building can be 700K SF, and yes, VD is addressed. (By the EE/Arch, EC, and AHJ)

As to resi....; sub-panel(s) are common, a lot of #12, and it has never become an issue that I am aware of.

BTW; we do a volt check at the service entrance, and base calcs on the 'available voltage', not the 'rated voltage'.

I also include 'basic' VD calcs in my class at the Vo-Tech.

John

HoseB611,

Can you give us more information on how this voltage drop rule is enforced or evaluated? Is it an amendment written into the code? Or an inspector enforcing the FPN that has been in the code for ages?

Do they mandate no more than 5% VD at the trip rating of the circuit? Or at the expected load on the circuit? How are short duration overloads (motor starting) evaluated. Must the circuit be sized sufficiently to start a large motor without 5% drop?

IMHO there is already an implied voltage drop requirement in the code, as a result of the 'effective ground fault current path' requirement. Soares interprets this as meaning that a short circuit must cause sufficient current flow to reach the 'instantaneous trip' range of the breaker. This means that at the end of the circuit, you want about 8-10x the trip rating of the breaker, implying a maximum voltage drop at the trip rating of about 10%.

-Jon

Quote --------------------------------------------
As an AHJ, I have to enforce the plans and specs, as they become part of the Electrical Permit, upon review and approvals.
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I'm a little surprised at this - I pretty much thought the local building inspector was strictly code compliance and not concerned with contract compliance.

It sounds more like the AHJ just bought a suretest

In New Zealand the supply characteristics as per AS/NZ3000:2000 are 1.8.2.
230/400 system ± 6%. 243.8V max. and 216.2 min.

under 1.8.4. I quote:
Unless an electrical installation is specifically designed to operate under reduced voltage conditions, the voltage drop between the point of supply and any point of the electrical installation shall not exceed 5% of the nominal voltage of the supply.

where Point of supply is: 1.4.71

The junction of the electricity distributor's conductors with the consumer mains.

Frequency value is not quoted here under 1.8.2. perhaps Mike can give the details here.
Under the 1987 regs appendix I. 1984. reg 14.
the frequency shall be maintained except for momentary fluctuations within ± 1.5% of the standard frequency e.g. 49.25 and 50.75 Hz. (for 50 Hz network.)

[This message has been edited by RODALCO (edited 01-20-2006).]

Radar & Gfretwell:

OK, I'm an Electrical Inspector, not Building. The State (NJ) mandates within the UCC that plans and specs submitted and approved for the permit be enforced. It's not a 'cowboy' thing.

Ie: Site lighting project; plans/specs require 3/4 x 10' grd rod at each pole base (29), #4 Cadwelded, 18" BFG.

Gfretwell....what's a "Suretest"????; NO I don't have one.

John

It was mentioned a few times in this post that a subpanel will provide voltage drop reduction.
Consider that a subpanel uses a relatively small feeder, and if there are a few loads on that subpanel, I would guess that voltage drop may be worse when the appliance can't draw directly from the service panel.

Radar inspection are handled differently in each area.

Where I am I have never had an inspector try to enforce the specs or prints.

At the same time the engineers know this and are either watching us directly or sending people out to watch us.

Personally I think this works well as they can come by anytime unexpectedly.

Bob

A Suretest is a handheld tester sold by Ideal that you usually see home inspectors using. Along with the usual ground/neutral checking it has a momentary voltage drop test using a 12a spike.

My concern with this type of thing as an inspector is you really need to know the load before you can compute voltage drop. I don't think it is reasonable to design every circuit for a 100% load at the farthest point.

2005 NEW MEXICO ELECTRICAL CODE States:
210.19 (A). General. Voltage drop. Add: “Conductors for branch circuits shall be sized to prevent excessive voltage drop. Conductors on 15 amp branch circuits, between the overcurrent protection device and the farthest outlet served, shall not exceed 75 feet for # 14 AWG copper circuit conductors, or 150 feet for # 12 AWG copper, measured along the branch circuit conductors. Conductors on 20 amp branch circuits, between the overcurrent protection device and the farthest outlet served, shall not exceed 75 feet for # 12 AWG copper, or 150 feet for # 10 AWG copper, measured along the branch circuit conductors. Branch circuits exceeding 150 feet from the overcurrent device to the farthest outlet served measured along the branch circuit conductors, shall be sized so that the voltage drop does not exceed 5%.”

The gov. must have lost a bet to the guy from COPPER.ORG

How are they enforcing this. Do they just guess how the wires are routed or do they bring a TDR? I suppose it is cheaper to just upsize +1 and hope they don't think you are over 150'.

HoseB:
Your State amendment sure sounds like what I see within specs doing plan review by some engineers.

As an AHJ, VD notes are checked on plan review; I/we do not 'measure' at field inspections. Basically, if #8 is on plans, that's what I/we look for.

John

I agree with Gfretwell....it looks to me like the AHJ has become facinated with the new testers out there.

You can be pretty sure the inspector isn't going to snake a tape measure along each wire to check its' length. Rather, he will simply plug in the latest 'whiz-bang' tester at what he thinks are the most remote receptacles, punch the "15 amp" button, and see what drop the meter reports.

Interesting as these meters are, I do not have one- simply because there are myriad other things calling for my money!

The meters are probably a good thing- I expect they will reveal more loss from bad connections than long wires- but making them a requirement is another thing altogether.

Why? If nothing else, is is not always clear just what a device tests for, nor are there always industry standard testing methods. The current debate over AFCI testers should caution everyone against blindly, enthusiastically accepting the latest marketing miracle.